This invention is related to systems for life support in avionics, in particular adjusting the anti-G suit and avionics antigravity system to prevent loss of consciousness, and also for crew member workload assessment.
Modern high performance aircraft and spacecraft operate at very high altitudes and acceleration rates. This may result to the effects of +Gz forces that exceed human tolerance levels, leading to G-force induced loss of consciousness (G-LOC). G-LOC results from critical reduction in cerebral blood flow. Acceleration may also affect vision at high G's. The effect of acceleration on vision depends on the direction of the force vector, +Gz acceleration (eye balls down) results in dimming of vision, followed by "tunnel vision" loss of sight which begins on the periphery and gradually narrows down until macular (central) vision remains. On the other hand -Gz acceleration (eyeballs up) results in diminished vision, redout (red vision), an increase in the time for the eyes to accommodate, and blurring or double of vision. This is followed by total blackout and then loss of consciousness. Other mild effects of gravitational forces include motion sickness and space adaptation syndrome.
The use of anti-G suits helps prevent these episodes, by applying pressure to the abdomen and lower extremities to restrict downward pooling of blood, and reduce the fall in cerebral blood flow. The inflation and deflation of the anti G-suit is controlled by valves. Air is filled into the bladders only at periods of high G's.
Usually anti G-suit valves, in use today are mechanically controlled, or inertial valves, providing pressurized air to the bladders at pressures proportional to acceleration. Electronic servo feedback mechanisms for quicker triggering of the anti-G valve as disclosed in U.S. Pat. No. 3,780,723, to Van Patten and U.S. Pat. No. 4,243,024, to Crosbie, et al. These documents use the rate of change of acceleration to set the threshold level for triggering the signal that initiates the inflation of the anti-G suit. U.S. Pat No. 4,336,590, to Jacq, et al. describes a microprocessor controlled anti-G suit valve that intitiates inflation of the air bladders on control stick movement indicating imminent high acceleration.
The patent to Robinson, No. 4,906,990, is upon an anti-G system failure detection, and shows means for regulating the pressure within a anti-G suit, for use in space flight. The patent to McStravick, et al, No. 4,817,633, discloses a light weight device to stimulate and monitor human vestibuloocular reflex. This device includes a helmet formed of a rigid shell, which is lined with various bladders that are subject to variations in pressure, for detecting degrees of acceleration, and for measuring head and eye movements, and their effects upon the neurosensory system of the wearer. The patent to McGrady, No. 4,799,476, discloses a univeral life support system, for use in air craft or space craft travel, and providing for variations in the transmission of gases and signals sent between the craft, and the seat in which the pilot sits, for providing input data to the life support control system of the air craft, to adapt the system to appropriate temperature and gas supply schedule The patent to Van Patten, No. 4,736,731, discloses a rapid acting electro-pneumatic anti-G suit control valve.
In addition, a book edited by Aaslid R, entitled "Transcranial Doppler Sonography," and published by Springer, of Wien, New York, dated 1989, on pages 39 through 50, describes the principle applied to measurement of blood flow velocity in cerebral arteries.
All the existing systems initiate pressure adjustment based on the physical parameter--acceleration, without consideration of physiologic changes in the human organism. Most importantly, the changes in cerebral blood flow are not monitored, so reductions, leading to loss of consciousness are not taken into consideration. Another disadvantage of increasing pressure in the extremities without consideration of the state of cerebral blood flow, is that this may lead to excessive increase resulting in a condition where blood supply exceeds demand and overall inefficient blood-brain exchange. The latter is an abnormal condition which may impair cortical function.
It is therefore desirable to have a system that triggers the anti-G suit pressure changes based on the assessment of the physiologic condition of the crew member in response to the changing environment.
An advantage of this invention is to provide a system that allows for individual tolerance level, since acceleration can produce varying effects from one individual to the other. This is of course dependent on the peculiarities of physiologic regulatory systems especially for blood pressure and cerebral blood flow.
Another object of this invention is that it allows individual workload assessment of crew members.